Welding of metal strips and tubing



Sept. 15, 1959 w. c. RUDD ETA!- 2,904,668

WELDING 0F METAL STRIPS AND TUBING Filed Oct. 7, 1958 2 Sheets-Sheet lINVENT M1. LACE CIR/0 50552 rJSrA NTDM M MQW AT TUBA [7J1 I Sept. 15,1959 w. c. RUDD ETAL I WELDING OF METAL STRIPS AND TUBING 2 Sheets-Sheet2 Filed Oct; 7, 195a INVENTORS M4 LACE C. E2100. 13255,??- JJrA/vm/v.

c r 2,904,668 Patented S P 1959 WELDING or METAL srnrrs AND rususcWallace C. Rudd, Larchmont, and Robert I. Stanton, Brooklyn, N.Y.,assignors to Magnetic Heating Corp., New Rochelle, N.Y., a corporationof New York Application October 7, 1958, Serial No. 765,869

Claims. (Cl. 219--67) This invention relates to methods and apparatusfor welding seams in metal tubing or the like and for the weldingtogether of the edges of strips or other metal portions. The inventionis particularly adapted f r the welding of metal portions which arerelatively thick along the edges or bands thereof which are to be weldedtogether.

This application comprises a continuation-in-part of applicantscopcnding application Serial No. 638,566, filed February 6, 1957 (PatentNo. 2,857,503 issued October 21, 1958) to which reference is herebymade, the present invention being directed to certain aspects of theapparatus referred to but not claimed in said copend ing application.

In accordance with the invention of said patent, longitudinal seams intubing or between the longitudinal edges of strips or other metalportions may be welded together as same are advanced past a weld pointby applying high frequency current thereto in advance of the weld point,which current flows along the edges to be welded for a sufficientdistance and with sufficient intensity prior to the weld point tobringthe edges to be welded up to welding temperature. The current is appliedto the edges by con tacts slidably engaging the metal adjacent to orbetween the edges.

But if the metal of the edges is relatively thick, there will be atendency for the current to become more concentrated along the upperportions of the edges if the contacts engage such upper portions, andthus the lower portions of the edges will not become heated to weldingtemperature upon reaching the weld point (or strictly speaking thevertical line at which the welding between the edges occurs and whichfor brevity will be herein referred to as the weld point). However, asexplained in connection with Fig. of said patent, if a strip or block ofhigh conductivity non-magnetic metal, such as copper, is placed along,below and adjacent the edges which are to be welded but in slightlyspaced relation thereto, then the impedance to the high frequencycurrent flowing in the metal portions to be welded and. which arenearest such high conductivity strip, will be substantially reduced ascompared with the situation which would prevail if such a strip or blockof copper were not present.

More specifically according to a preferred embodiment .of the presentinvention the terminals of a high frequency current source are appliedto contacts which engage respectively exposed surfaces on opposite sidesof a narrow V-shaped gap between the advancing metal portions to bewelded so that the path of current thereon is from such contacts, alongon the gap edges to and from the weld point. And in order to cause suchcurrent to flow over the full depth of the edges in such V-shaped gap, a5

block of metal of high conductivity, such as of copper or the contactsengage the upper surfaces of the approaching gap edges, then the highconductivity block or strip is positioned closely beneath the undersideof the gap.

Contrary to what might be assumed from superficial consideration of thematter, the use of such non-magnetic high conductivity blocks or stripsin the manner above referred to with currents of the high frequencieshere involved is surprisingly effective in reducing the impedance of theadjacent metal portions. to be welded and thus high y effective incausing the current to flow over the full depth of the edge surfaces andthus causing them to be uniformly heated to the requisite weldingtemperature. On the other hand, if similar blocks or strips but ofmagnetic material are provided in accordance with other and quitediiierent aspects of the invention of said patent, then the eiiect issubstantially the opposite from that attainable with strips of highconductivity non-magnetic metal, that is, the impedance of the metalportions adjacent thereto will be greatly increased rather than beingdecreased.

In the welding of tubing having walls or strips which are relativelythick, the metal as a consequence will be relatively rigid and as themetal portions are advanced to and past the weld point the portionscannot be easily held deflected apart in advance of the weld point byany substantial distance or so as to come together at any verysubstantial angle such as would afford the possibility of placing thehigh frequency contacts down into a gap therebetween to try to ensureproper current flow along both the upper and lower portions of the edgesto be welded. Thus with such relatively thick metal it is difficult orimpossible to apply the high frequency contacts other than to theexposed surfaces outside the gap. For these reasons the presentinvention makes possible the welding of thick-walled tubes or thickstrips which could not otherwise be. welded by the general methods hereinvolved, at least uniformly and efliciently, throughout the depth ofthe weld. While it would be possible to start applying the current sofar in advance of the Weld that the edges might be heated to weldingtemperature throughout their depth, the heating would still not beuniform to the full depth of the edges and also the heating time wouldthen be so long that there would be a considerable wasteful thermal flowinto the metal to' regions remote from the desired line of the weldedseam or else the parts to be Welded would have to be advanced sorelatively slowly that similar difiiculties would occur. With thepresent invention, however, proper heating to the full depth of the seamis made possible at high speed and with the contacts located as close asfrom 2 to 4 inches, in typical cases, in advance of the weld point andthus the heating time is so brief that flow of heat into metal away fromthe line of the seam is minimized.

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below, taken inconnection with the accompanying drawings illustrating byway of examplea preferred form of the invention.

In the drawings:

Fig. 1 is a perspective and somewhat schematic view illustrating theprincipal features of the invention;

Fig. 2 is a vertical sectional view, the section being taken through theline of the desired seam to be welded, and the current flow to the fulldepth of the seam as made possible by the invention being indicated bydotted lines;

Fig. 3 is a perspective view showing the high conductivity element usedin the apparatus; and

Fig. 4 is a view similar to Fig. 2 but illustratingby dottedlines thegeneral pattern of the current flow which will occur when the presentinvention is not utilized.

Referring to the drawings in further detail, a length 'of metal tubingis indicated at 10 as it advances in the "2,904,668 t v e directionindicated by the arrow through a tube mill having pressure rollers as at11, 12 of a known type for pressing the tube edges which are to bewelded together into contact at or adjacent the weld point w. That is,in practicing the invention in the manner shown in Fig. 1, the tubing asit advances has previously been shaped in generally tubular form but hasa longitudinal gap 13 and in cases such as here involved where the metalis relatively thick, such gap will generally be quite narrow, forexample, in the neighborhood of inch and too small to permit the currentapplying contacts to be located therein. The pressure rollers, such asindicated at 11, 12, or some other equivalent means serve not only tobring the gap edges together at or adjacent the weld point but also, ifdesired, to advance the tubing at a high rate of speed which may varyunder different conditions, for example, from several feet per minute toabout 100 feet per minute.

' According to the embodiment of the invention shown in Fig. 1, heatingcurrent of a radio frequency is brought from a suitable current sourceand its terminals connected respectively to contacts 14, 15 which, asexplained in the above-mentioned patent, should be suitably fluid cooledas by fluid-cooling cavities therein as indicated. Thus the highfrequency will flow respectively from these contacts along theapproaching gap edges to and from the weld point w, but if no furthermeasures are taken, such current would tend to be more or lessconcentrated along the upper portions of the approaching gap edges asindicated by dotted lines 16 in Fig. 4. To avoid this difficulty and tocause the current flow to extend over the full depth of the edges asshown by the dotted lines at 17 in Fig. 2, a mass, block or strip ofhigh conductivity nonmagnetic material as at 18 is positioned to extendalong in closely spaced relation to and beneath the gap. This strip may,for example, be formed of high conductivity copper, silver or othermaterial having high conductivity.

As indicated in Fig. 3, the member 18 is preferably fluid cooled, forexample, by use of water inlet and outlet connections 19 and 20communicating with a cavity 21 in the member. These connections may alsobe used as supports for the member and may extend into and up through asuitable gap spreader means 22 of a known type (Fig. 2) which will actas a support for the member 18. Suitable supporting means (not shown)for such spreader may be provided preferably of a form which will beadjustable in vertical and horizontal directions as indicated by thearrows 23.

It will be understood that similar equipment similarly arranged may beused for welding together two advancing strips or other metal portions,that is, the two strips would be advanced with a narrow V-shaped gaptherein preceding the weld point where the pressure rolls would pressthe strips firmly into welding engagement in the manner indicated inFigs. 12-17 of the abovementioned patent.

While sometimes herein and in the appended claims reference is made tothe upper and lower" surfaces of the metal portions to be welded, itwill be understood that these terms are used relatively, that is to say,to identify the relative positions of the surface portions intended andas shown in the accompanying drawings, it being understood that theequipment might be mounted in various positions with respect to thefloor level and different from or even inverted as compared with themanner in which same is here shown.

The invention is particularly well adapted for Welding tubing having awall thickness or strips having a thickness of, for example, 4 inch upto /2 inch or more and in typical cases as above noted, the contacts 14,15

.may be spaced back from the weld point by a distance of about 2 inchesup to 4 inches in which event the width of the V-shaped gap at thecontacts would be in the neighborhood of A inch more or less and thustoo narrow to permit placing the contacts down within the gap.

The high conductivity member 18 in typical cases may be adjustablypositioned, for example, at a distance preferably in the neighborhood ofA inch below the lowest portions of the edges to be heated and suchmember should extend forwardly from the region beneath the contacts 14,15 to a region which is beneath the weld point or thereabouts. Themember 18 may be of a width such as to overlap the width of the gap ateach side by about Mr inch more or less in typical cases.

As specified in the above-mentioned patent, the current used ispreferably of a radio frequency, such, for example, as a frequency ofthe order of 100,000 cycles per second or up to 300,000 to 400,000cycles per second or higher. As the frequency is increased above about50,000, the efficiency of the method and quality of the weld is rapidlyimproved for the reason that the heating to welding temperature becomesmore and more concentrated (according to a square root relation) withinan extremely thin layer of the metal on the very edge surfaces to bewelded, leaving the metal in back thereof firm so that the weldingsurfaces may be very effectively forged together without noticeabledisruption of the crystalline structure of the metal. The method andapparatus of this invention are especially well adapted for the weldingof steel tubing or strips, but may also be used with advantage forwelding copper or aluminum or alloys thereof, among other metals.

While the invention has been described above as applied to the weldingof metal portions as separated by a narrow V-shaped gap (such as the gapshown with the apparatus of Figs. 12-17 of the above-mentioned patent)and with the opposite terminals of the current source applied toopposite sides of said gap, some advantage may be obtained by practicingthe invention with the alternative contact arrangements and with the gapclosed or open as in other figures of said patent.

Upon adjusting the proximity of the high conductivity member 18 withrespect to the metal portions to be welded, it will be understood thatthe depths to which the current flows on the thick edges with fullintensity may be varied so that, for example, the outer portions of theweld on a length of tubing may be heated and softened slightly more thanthe inner portions of the weld While still bringing such inner portionsup to welding temperature (or the reverse may be accomplished) wherebythe upset of the weld may be largely directed upwardly or, if preferred,downwardly.

Although certain particular embodiments of the inventron are hereindisclosed for purposes of explanation, further modifications thereof,after study of this specification, will be apparent to those skilled inthe art to which the invention pertains. Reference should accordingly behad to the appended claims in determining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. Method for welding a seam extending along opposed edges of tworelatively thick elongated metal portions, which comprises: advancingsaid portions with their said edges passing along the line or" thedesired seam and past a weld point; firmly retaining said edges togetheras they reach the region of such weld point; conducting high bymaintaining near the undersurfaces of said metal portions and adjacentsaid edges a mass of non-magnetic highly conductive material effectiverelatively to decrease the reactance of the current paths on the lowerportions of said edges as compared with the reactanc'e,

for said high frequency, of the upper portions of said edges.

2. Method for welding together the edges adjacent a longitudinal gap inmetal tubing having relatively thick walls, which method comprises:advancing the tubing with said edges passing along the line of thedesired welded seam and past a weld point; firmly retaining said edgestogether as they reach the region of such weld point; conducting highfrequency current onto the outer surface of the tubing adjacent saidline and in advance of said weld point to maintain over a distancesubstantially in advance of said weld point flows of said current forprogressively heating said edges up to welding temperature when samereach said weld point, and causing said flows of current to extend oversubstantially the full depth of said edges by maintaining near the innersurface of the tubing adjacent said edges a mass of non-magnetic highlyconductive material effective relatively to decrease the reactance ofthe current paths on the inner portions of said edges as compared withthe reactance, for said high frequency, of the outer portions of saidedges.

3. Method for welding together the edges adjacent a longitudinal gap inmetal tubing having relatively thick walls, which method comprises:advancing the tubing with said edges passing along the line of thedesired welded seam and with a narrow V-shaped gap therebetween, andthence past a weld point; firmly retaining said edges together as theyreach the region of such weld point; applying electrodes connectedrespectively to the terminals of a high frequency current source ontoouter surfaces of the tubing on opposite sides of said gap and inadvance of said weld point to maintain over a distance substantially inadvance of said weld point flows of said current from the electrodes toand from the weld point for progressively heating said edges up towelding temperature when same reach said weld point, and causing saidflows of current to extend over substantially the full depth of saidedges by maintaining near the inner surface of the tubing and adjacentsaid gap a mass of non-magnetic highly conductive material effectiverelatively to decrease the reactance of the current paths on the innerportions of said edges in the gap as compared with the reactance, forsaid high frequency, of the outer portions of said edges in the gap.

4. The apparatus for welding a seam extending along opposed edges of tworelatively thick elongated metal portions, comprising in combination:means for advancing said portions with their said edges passing alongthe line of the desired seam and past a weld point; opposed means forpressing said portions together whereby their said edges are firmlyretained together as same pass the region of such weld point; contactsadapted to be connected to the terminals of a source of high frequencycurrent, said contacts being positioned to engage upper surfaces of saidmetal portions adjacent the said line for conducting such high frequencycurrent onto said portions to maintain over a distance substantially inadvance of said weld point flows of said current for progressivelyheating said edges up to welding temperature upon reaching said weldpoint; and means for causing said flows of current to flow over the fulldepth of said edges, said latter means comprising a mass of non-magnetichighly conductive material mounted in proximity to the undersurfaces ofsaid metal portions and adjacent said edges, such mass being effectiverelatively to decrease the reactance of the current paths on theportions of said edges nearest said mass as compared with the reactance,for said high frequency current, of the upper portions of said edges.

5. The apparatus for welding together the edges adjacent a longitudinalgap in metal tubing having relatively thick walls, such apparatuscomprising in combination: means for advancing the tubing with theirsaid edges passing along the line of the desired seam and with a narrowV-shaped gap therebetween, and thence past a weld point; opposed meansfor pressing said edges together as same reach the region of such weldpoint; contacts respectively adapted to be connected to the terminals ofa source of high frequency current, said contacts being positioned toengage outer surfaces of the tubing at opposite sides of said gap forconducting such high frequency current to flow from said contacts alongon said edges to and from the weld point to maintain over a distancesubstantially in advance of said weld point flows of said current forprogressively heating said edges up to welding temperature upon reachingsaid weld point; and means for causing said flows of current to flowover substantially the full depth of said edges, said latter meanscomprising a mass of non-magnetic highly conductive material mounted inproximity to the inner surfaces of the tubing and adjacent said edges,such mass being effective relatively to decrease the reactance of thecurrent paths on the portions of said edges in the gap nearest said massas compared with the reactance, for said high frequency current, of theouter portions of said edges in the gap.

References Cited in the file of this patent UNITED STATES PATENTS2,024,906 Bennett Dec. 17, 1935 2,066,668 Bennett Jan. 5, 1937 2,833,910Stanton et a1. May 6, 1958

